Booster structure



J 24 19 9 vD. J. DITTMANN' 51 1 BOOSTER STRUCTURE Filed Sept. 22, 1967 FIG. 4A

DAVID J. DITTMANN INVENTOR.

ATTORNEY 3,451,341 BOOSTER STRUCTURE David J. Dittmaun, Woodstock, N.Y., assignor t Hercules Incorporated, Wilmington, Del., a corporation of Delaware Filed Sept. 22, 1967, Ser. No. 669,737 Int. Cl. F42b 3/10 US. Cl. 102-24 17 Claims ABSTRACT OF THE DISCLOSURE A booster type initiator for explosives is provided which contains a Well and a flange around the open end thereof, of integral resilient material construction, as a combined Well and end closure assembly therefor; and in preferred embodiments (l) rib structure integral with the well member and extending along the inner wall thereof, for support of a primary initiator and (2) a bail member integral with the flange and extending therefrom for emergency removal of the booster from a complete blasting assembly. Said integral well and flange structure per se is also provided.

This invention relates to a flange and well member of integral resilient material construction, for emplacement in booster type initiators for explosives, as a combined end closure and well assembly therefor. In one aspect this invention relates to booster type initiator assemblies for explosives containing the integral flange and well member structure, above described, as a combined end closure and well assembly. In another aspect this inven tion relates to booster type initiators that can be manufactured more economically than heretofore by incorporating the booster shell closure and well elements as an integral unit formed from a resilient material. In another aspect this invention relates to booster type initiators in which the above described integral structure is formed from a water deteriorable material, so as to be self-disarming in response to deteriorative action of water after a misfire in a water environment. In another aspect this invention relates to booster type initiators containing integral structure above described, and also integral therewitth a tab member extending upwardly from the closure, as a bail member, for emergency removal of the booster assembly from the main explosive system normally ready for firing. In still another aspect this invention relates to booster type initiators containing integral well structure, above described, and also integral therewith, rib structure on the inner wall of the well member to frictionally support a primary initiator therein. Other aspects of the invention will be apparent in light of the accompanying disclosure and the appended claims.

Complete explosive assemblies constitute a combination of main explosive charge, with means for initiating detonation of same. One such type of assembly constitutes a combination of main cap-insensitive explosive charge, a secondary initiator, and a primary initiator. The secondary initiator (containing a booster charge) is detonated in response to initiation of the primary initiator (an electric blasting cap or a detonating fuse) and the main charge is detonated in response to detonation of the booster charge to provide the full explosive force of the main charge.

A typical and generally utilized primary initiator is an electric blasting cap of either the instantaneous or the delay type, numerous designs of which are well known in the art. Another type of well known primary initiator is a detonating fuse, i.e., a plastic covered core of a high explosive such as PETN, Primacord being one such 3,451,341 Patented June 24, 1969 type initiator. A typical and generally utilized secondary initiator is a booster cartridge containing a high explosive as a booster charge, and a well for supporting a primary initiator in detonating relationship therewith. The secondary initiator is generally supported in detonating relationship with the main charge in a well extending into the main charge of a complete explosive assembly.

Heretofore, such booster type initiators have generally comprised a closed metal booster shell substantially filled with booster charge, a metal well member extending into the shell through one end thereof and terminating in contact with the booster charge for support of the primary initiator, and a seal type material in closing relationship with the annulus formed, in the end of the shell, through which the well extends, by the inner wall of the booster shell and the outer wall of the well member. The fabrication of such booster assemblies has required separate steps for installation of the individual booster seal and well components, each of the steps requiring precision control. Such fabrication methods have, of course, been uneconomic from the standpoint of manpower, equipment, and time requirements, and accordingly the art has necessarily been committed to the inherently high costs involved.

Further, general practice has been to stake or dimple the well member of the booster so that when the primary initiator is inserted therein the dimple or stake serves as a restraining means to retain the primary initiator in operating position within the well. Such restraining means has however not been entirely satisfactory. This has been due, particularly, to the loss of resiliency in the dimple or stake.

After initial emplacement of a booster type initiator in a complete explosive assembly, i.e., in the booster well in the explosive cartridge, it is often necessary to remove, and/or replace the booster initiator for various reasons associated with the particular shooting operation. Accordingly, it has been the practice to adhere a paper tab to the outside of the booster shell to serve as a bail for the booster in the event it is for any reason to be removed. This has often been unsatisfactory due not only to failure of the tab, but also to failure of the adhesion--and particularly after the booster has been emplaced over an extended period.

In the emplacement of a complete explosive assembly in a water-covered area, e.g., during offshore seismic exploration, there are often failures in the system caused by damage imparted to the communication lines, with accompanying loss of the assembly. The result in all events is a misfiring, i.e., failure to shoot; and in such instances of misfiring the assembly remains live, uncontrolled, and therefore retrievable with great difficulty if at all.

Such misfiring in Water-covered areas presents serious safety hazards. In many such instances the complete assemblies, or components separated therefrom, still live but out of control, are eventually washed ashore and are subject to accidental firings to impair the safety of persons and property in the adjacent shore area. In view of such hazards, local authorities have in many instances deemed it necessary to halt exploration taking place off their shores until there can be assurance that explosive assemblies or components thereof resulting from misfirings will not impair the safety of their shore areas. It is of utmost importance therefore that any such component or components of an assembly subsequent to a misfire in a Water-covered area be self-disarming so as to become harmless and hence no longer constitute a safety hazard.

This invention is concerned with booster type initiators that can be fabricated in accordance with a single operating step and hence are more economically attractive to the art than heretofore; and which, optionally, contain improved support means for the primary initiator, 'and/ or improved bail structure for emergency removal of the booster from the complete assembly, and/or which are self-disarming after a misfire in a water environment. The invention is further concerned with a well and end closure assembly of integral construction as an element of the above described booster assemblies.

In accordance with the invention, a combined well and end closure for a booster type initiator assembly is provided which comprises a tube closed at one end to form said well member and a flange entirely around an open end portion of said tube to form said end closure when said well is emplaced in said booster assembly; and said tube and said flange constituting an integral unit of resilient material; Further in accordance with the invention,

a booster type initiator assembly is provided which comprises an elongated shell closed at one end, and a booster type explosive charge within said shell; a tube closed at one end to form: a well member for said assembly and a flange entirely around an open end portion thereof, and said well member and said flange constituting an integral unit of resilient material as a combined well and end closure for said booster assembly, as described hereinafter; said integral well and flange unit being disposed within said shell and extending therein, closed end first, from an open end portion of said shell into operative communication with said explosive charge to support a primary initiator therefor; and said flange being disposed along its entire periphery in contact with the inner wall of said shell forming said open end portion in watertight closing relationship with said shell.

In now preferred practice the well member contains as an integral part thereof at least one rib element extending outwardly from, and longitudinally along, the inner wall thereof to frictionally engage a primary initiator as a support therefor to restrain it from movement after emplacement. Generally, from two to three such rib members uniformly spaced apart are preferred. In now preferred practice, the integral closure and well structure also contains, as an integral part thereof, a tab formed of the same material and extending upwardly, i.e., in an axial direction, from the integral unit as a bail member for the booster assembly for emergency removal of same after emplacement.

In accordance with another embodiment, the integral closure and well structure, above described, is formed from a water-deteriorable material which, after a preset period of time in a water environment, dissolves or disintegrates in response to contact with the water to permit ingress of water into the shell to desensitize the charge and/or wash it from the shell, and hence render the booster harmless.

The invention is illustrated with reference to the drawings of which FIGURE 1 is an elevation of the booster assembly of the invention in which the well and end closure members are of integral construction, and are formed from a resilient material, optionally a water-deteriorable material to provide for self-disarming of the assembly in event of a misfire in a water environment; FIGURE 2 is a perspective view of the integral well and closure construction, per se, of FIGURE 1; FIGURE 3 is an elevation of the integral construction of FIGURE 2 except that it additionally illustrates rib structure in the well member for support of a primary initiator therein, and FIGURE 3A is a view taken along the line 3a-3a of FIGURE 3 further illustrating the rib structure of FIG- URE 3; FIGURE 4 is a perspective view the same as that of FIGURE 2 except that it additionally illustrates a tab member extending upwardly from the booster end closure element as a bail for emergency removal of the booster assembly from emplacement in a complete explosive assembly ready for firing, and FIGURE 4A is a 4- view taken along the line 4a4a of FIGURE 4 further illustrating the tab structure of FIGURE 4.

Referring to FIGURE 1, booster type initiator assembly 10 comprises elongated metal shell 11, closed at bottom end 12 and open at top end 13, and containing a convention cap-sensitive booster type explosive charge 14, such as PETN, tetryl, pentolite, composition B, cyclonite, or the like.

Tube member 16, closed at one end 19, and open at the other end, is a primary initiator well member for booster assembly 10, and is formed from a resilient material; and flange 17, also formed from a resilient material, is disposed entirely around the open end of tube 16 and is integral therewith. Well member 16- and flange 17 constitute an integral unit of resilient material as a combined well and end closure for assembly 10. Integral unit 18 is disposed within shell 11 and extends therein, closed end first, from open end portion 13a of shell 11, generally an endmost portion, into operative communication with explosive charge 14 to support a primary initiator therefor. Generally, well member 16 is in direct contact, at least at closed end 19, with charge 14', and preferably along substantially its entire length. Flange 17 is in direct contact along its entire periphery with the inner wall of shell portion 13a in watertight closing relationship with shell 11.

Flange 17 and well member 16, as an integral unit of construction, can be formed from any suitable resilient or plastic material. Polyethylene is a now preferred plastic material for the formation of the integral well closure unit 18, which is advantageously carried out by injection molding. Other suitable plastic material from which the integral unit 18 can be formed include polypropylene, polyimides such as nylon, polystyrene, polyvinyl chloride, and the like. Thermoplastic elastomers such as styrenebutadiene copolymers are particularly preferred resilient materials when the integral end closure and well assembly is to be crimped in closed relationship with the booster shell, whereas high density polyethylene is preferred when the unit is to be force fit into the shell. When the integral end closure and well assembly is to be supported in closing relationship by adhesion, a thermosetting material such as Bakelite or other suitable phenolic material is preferred. In those instances wherein the booster assembly is to be utilized in a water environment, and particularly in offshore seismic exploration, the now preferred resilient material of construction for the integral closure and well structure is a water-deteriorable material such as Klucel (hydroxypropyl cellulose containing at least two hydroxypropyl groups per anhydroglucose unit), CMC (carboxymethylcellulose), poly(vinyl alcohol), and the like.

In one embodiment, a suitable plastic, e.g., polyethylene is injection molded to form integral unit 18 which is then forced into shell 11, well member 16 first, until it is emplaced with flange 17 in closing relationship with the open end portion 13a of booster shell 11, as above described. Generally, the booster shell is cylindrical and is from about 1 to 5 inches in length and has a diametric cross section of from about /2 to 4 inches. Well member 16, and flange member 17 are cylindrical and well member 16 extends into shell 11 a distance in the order of from about A to A the length of shell 11 and forms a resulting annulus, i.e., between the well member and the booster shell, having a width (normal to the shell axis) of about /8 to A of the diametric cross section of shell 11. The integral unit 18 is force fit into the end of shell 11 and is therefore initially of slightly greater cross sectional dimension than that of shell 11 to assure the necessary compression of the flange for a watertight force fit.

In FIGURE 2 wherein primed index numbers refer to like parts in FIGURE 1, identified by the same but unprimed index numbers, is shown integral well closure unit 18' which is a perspective view of the integral unit 18 of FIGURE 1. Generally, the well and flange members of integral unit 18' are cylindrical in shape and flange member 17 is from about /2 to 4 inches in diameter at a depth, or wall thickness, of from A to inch, and well member 16' is from 1 to 4 inches in length and has an inside diameter of from 0.2 to 0.4 inch and a wall thickness of from about 0.010 to 0.050 inch. Well 18' is preferably pointed at the end 19' to facilitate its penetration into the booster charge during emplacement in the booster assembly.

With reference to FIGURES 3 and 3A, wherein double primed index numbers refer to like parts in FIG- URE 2 identified by the same, but single primed index numbers, is shown integral well and end closure assembly 18" which is an elevation of assembly 18' of FIG- URE 2 except that it additionally contains rib members 21a, 21b and 210 longitudinally extending along, and on, the inner wall 20 of well member 16", say in the order of from 1 to 2 inches. Rib members 21a, 21b and 210 formed from a resilient material are integral with the assembly 18" and are advantageously fromed as part of the entire assembly 18" by injection molding.

Rib members 21a, 21b and 210 are advantageously equispaced about the surface of the inner wall 20 of well member 18", i.e., about every 120. Each rib member extends toward the interior of the wall member a suflicient distance, say 0.010 to 0.025 inch to frictionally engage the primary initiator to restrain it from movement when it is emplaced in well member 16". Due to the resilient nature of the rib members, they are somewhat elastic and hence are slightly compressed, when in an engaging position with the primary initiator, to thereby compensate for any loss in restraining capacity that would be characteristic for such rib members formed from a nonresilient material. FIGURE 3A is further illustrative of the rib member structure 21a, 21b and 21c of FIGURE 3 and particularly illustrates the preferred equidistant spacing of those members.

Referring to FIGURE 4 and 4A wherein triple primed index numbers refer to like parts of FIGURE 2 identified by the same but less primed index numbers, is a perspective view of an integral well closure unit 18" of the invention which is the same as assembly 18' of FIGURE 2 except that additionally shown is a tab, or bail, member 24 attached to flange member 17" and extending upwardly (in an axial direction) therefrom to serve as a bail for the emergency removal of the booster assembly from emplacement in an explosive assembly. FIGURE 4A, a view taken along the line 4-4 of FIGURE 4, further illustrates the bail member 24 structure.

The integral closure and well structure of the preferred assembly is formed by injection molding of polyethylene; and it includes a plurality of rib members along the inner wall of the well member as illustrated with reference to FIGURES 3 and 3A, of the drawings, and often, a bail member as illustrated with reference to FIGURES 4 and 4A.

An exemplary and now preferred booster assembly of the invention is one formed from a cylindrical metal (copper, aluminum, brass, or the like) booster shell of 0.624 inch inside diameter, 0.648 inch outside diameter and 4.5 inches in length; and containing about 22 grams PETN, tetryl, pentolite, composition B, RDX, or the like, as the booster charge. The integral well flange element of the exemplary assembly is formed by injection molding of polyethylene. The seal, or flange, element, is force fit in the shell with an interference of 0.010 inch for a depth, or wall thickness, of 0.275 inch, and the well member is 2% inches in length, 0.315 inch inside diameter at the open end and tapered to 0.285 inch at the closed end (due to injection molding procedure) and has a Wall thickness of 0.030 inch. Three rib members extend longitudinally along a centralmost portion of the inner wall of the exemplary well member and are equispaced, i.e., at about 120. They extend from the inner wall of the well member to the interior of the well a distance of about 0.015 inch and are about 1% inches in length. A bail member extends upwardly from the flange element, formed of the integral well and closure, the ribbed, structure, and is an integral part thereof as above described. It is generally in shape of a ribbon having a thickness preferably in the order of from 0.020 to 0.30 inch, say 0.025 inch, a Width of from about 0.4 to 0.6 inch and a length of from about 0.4 to 0.6 inch, say about 0.5 inch.

As above described, it is an important feature of the invention that the integral closure and well structure of the booster assembly can be formed from a water-deteriorable material to provide for disarming. In that embodiment, the depth, or wall thickness, of the flange, and the wall thickness of the well member, are correlated with the rate of water deterioration of the particular material from which the integral unit is fabricated to permit the structure to resist deteriorative action of water and maintain its watertight relationship with the booster shell during a preset period for normal firing, beginning when the assembly is initially placed in the water environment, and to thereafter erode in response to said deteriorative action when the assembly remains undetonated in said environment, to destroy the watertight relationship and thereby permit ingress of water into the booster shell. Upon yielding of the well closure structure to the deteriorative action of water, the resulting water ingress provides for contact of water with the high explosive with accompanying densensitization, but, more significantly, for a substantially washing action to remove the solid high explosive from the shell, so as to, in either event, render the booster harmless.

Although as illustrated 'with reference to the drawings, the flange member is force fit into the booster shell, it is within the scope of the invention to effect the watertight relationship between the seal member and the shell wall by any suitable means such as by a conventional crimp, or by adhesion.

In now preferred practice the booster shell of the booster type initiator assembly of the invention is cylindrical and is from 1 to 5 inches in length and has an inside diameter of from /2 to 2 inches, often within the range of from /2 to 1 inch.

The integral well bail and closure structure of the invention can be emplaced in the booster assembly in a single step whereas heretofore three separate steps have been required/Thus, in the past it has been necessary to first emplace the 'well member in the shell, then apply a seal in the annulus between the well and the inner shell wall and, finally secure a suitable tab in the shell. As already described, the integral -well and flange unit, including the bail member when desired, can be emplaced in the booster shell in a single step operation. The invention therefore eliminates the need for a three-step operation and hence markedly reduces requirements for manpower equipment and time to which the art has been committed heretofore.

Further, the booster assemblies of the invention have only one seal, i.e., between the flange and the shell wall and are, accordingly, less susceptible to accidental failure than those of the prior art which require at least one additional seal.

What I claim and desire to protect by Letters Patent 1s:

1. A booster type initiator assembly comprising an elongated metal shell closed at one end and having a length of from about 1 to 5 inches and a maximum linear crosssectional dimension of from /2 to 4 inches; a booster type explosive charge within said shell; a tube closed at one end and having a wall thickness of from 0.01 to 0.05 inch, a flange entirely around an open end portion of said tube and having a wall thickness of from A to inch, and said tube and said flange constituting an integral unit of resilient material as a combined well and end closure for said booster assembly, as described hereinafter; said integral well and flange unit being disposed within said shell and extending therein, closed end first, from an open end portion of said shell into operative communication with said explosive charge to support a primary initiator therefor; and said flange being disposed along its entire periphery in contact with the inner wall of said shell forming said open end portion in force fit watertight closing relationship with said shell.

2. In a booster type assembly of claim 1, a plurality of rib members, integral with said well and flange unit, and extending longitudinally along the inner wall of said well member.

3. In a booster type assembly of claim 1, a bail member integral with said flange and well member, and extending from said flange in an axial direction from said booster assembly.

4. In a booster assembly of claim 1, said resilient material being a water-deteriorable plastic, and the wall thickness of said flange and said well member being correlated with the rate of water deterioration of said resilient material to cause said integral unit to resist deteriorative action of water sufficiently to maintain its watertight relationship with said booster shell during a preset period of time beginning when said assembly is initially placed in a body of water, and to thereafter erode to destroy said watertight relationship in response to said deteriorative action when said assembly remains undetonated in said body of water.

5. A booster type assembly of claim 4, wherein said water-deteriorable material is a hydroxypropyl cellulose containing at least two hydroxypropyl groups per anhydroglucose unit.

6. A booster type assembly of claim 1, wherein said resilient material is polyethylene.

7. A booster type assembly of claim 1, wherein said elongated shell is cylindrical.

8. A booster assembly of claim 7, wherein the diametric cross section of said shell is from /2 to 2 inches.

9. In an assembly of claim 8, a plurality of rib members extending longitudinally along the inner wall of said well member, and integral therewith.

10. In an assembly of claim 9, three said rib members equispaced along the wall of said well; and each rib member being about 1 to 2 inches in length and extending from said wall toward the interior thereof a distance of from about 0.010 to 0.025 inch.

11. In an assembly of claim 10, a bail member integral with said flange and well member, and extending from said flange in an axial direction away from said booster assembly.

12. In an assembly of claim 11, said explosive charge being selected from the group consisting of PETN, pentolite, composition B, tetryl and RDX.

13. In a booster assembly of claim 7, said resilient material being a water-deteriorable plastic, and the wall thickness of said flange and said well member being correlated with the rate of water deterioration of said resilient material to cause said integral unit to resist deteriorative action of water sufliciently to maintain its watertight relationship with said booster shell during a preset period of time beginning when said assembly is initially placed in a body of water, and to thereafter erode to destroy said watertight relationship in response to said deteriorative action when said assembly remains undetonated in said body of water.

14. A booster assembly of claim 13 wherein said waterdeteriorable material is a hydroxypropyl cellulose containing at least two hydroxypropyl groups per anhydroglucose unit.

15. A booster assembly of claim 7 wherein said resilient material is polyethylene and said integral well and end closure unit is a product of injection molding.

16. A booster assembly of claim 14 wherein the diametric cross section of said shell is from /2 to 2 inches.

17. A booster assembly of claim 15 wherein the diametric cross section of said shell is from /2 to 2 inches.

References Cited UNITED STATES PATENTS 2,755,735 7/ 1956 -Harter 102-24 2,909,121 10/1959 Gernart et al. 102--24 X 3,276,371 10/1966 Newman et al. 10224 3,276,372 10/ 1966 Cerwonka 102--24 3,279,372 10/ 1966 Patterson 1022 8 3,348,483 10/1967 Sorg 10224 3,356,021 12/ 1967 Driscoll et al 1022-8 FOREIGN PATENTS 1,215,193 11/1959 France.

VERLIN R. =PENDEGRASS, Primary Examiner. 

